Efficient activation of peroxydisulfate by 3D flower spherical-like Fe-NC for organic contaminant removal: Fe(IV)=O as a dominant species

The high-valent iron-oxo species (Fe(IV)--O) exhibit great prospects for the removal of organic contaminants in iron-mediated persulfate activation. Nevertheless, an adequate research of the mechanisms involved in Fe(IV)based activation processes and organic degradation remains elusive. Here, an Fe encapsulated in N-doped carbons catalyst (2Fe-NC) with three-dimensional flower shape and mesoporous structure was developed, which can 100 % remove various organic pollutants such as chloramphenicol (CAP), sulfamethoxazole, amoxicillin, benzoic acid, and bisphenol A within 30 min by peroxydisulfate (PDS) activation. In the oxidation system, 2Fe-NC as an electron transfer medium was critical to mediate electron transfer from organic compound to PDS, accompanied by the redox cycle of Fe(IV)/Fe(II) and Fe(IV)/Fe(III). Multiple experiments reveal that the oxidation mechanism of 2Fe-NC@PDS system is similar to the dioxygen activation mechanism of binuclear active sites, which activates PDS to form surface-active Fe(IV)--O species without producing radicals. The two pathways of CAP degradation simulated by density functional theory calculations release 6.92 and 4.23 eV, respectively, which is thermodynamically favorable. Overall, the new insights gained in this work offer a significant route to design more effective advanced oxidation processes for refractory contaminant treatment.